Deposition of thin metal films

ABSTRACT

An electroless process for depositing elemental metallic coatings on solid substrates. The process comprises forming a hydride of the primary metal to be deposited in situ on a substrate and subjecting the metal hydride to sufficient energy to deposit the elemental form of the metal on the substrate.

I Muted States Patent 1 1 1111 3,762,938

Ridenour et al. Oct. 2, 1973 [54] DEPOSITION 0F THIN METAL FILMS 3,578,494 5/1971 Williams et a1 1 17/160 R v 3,041,197 6/1962 Berger ..117/160 R X [751 Inventors- R'dmd P" Kenna/h 3,449,150 6/1969 Williams et a1. 117/160 R x Groves, Midland, Mlch- 3,549,412 12 1970 Frey, Jr. et a1 117/160 R x [73] Assigneez The Dow Chemical Company, 3,563,787 2/1971 Schneggenburger et al.117/160 R X Midland, Mich- FOREIGN PATENTS OR APPLICATIONS [22] Filed: Mar. 29, 1971 2,454 4/1957 Japan 1,319 2/1964 Japan [21] Appl. No.: 129,204 9,660 6/1964 Japan Related US. Application Data [63] Continuation-impart of Ser. No. 783,164, Dec. 6, Primary Exam".'er Alfred Leavm 19 g abandoned Asszstant ExammerJ. R. Batten, Jr.

Attorney-Griswold & Burdick, Robert W. Selby and [52] US. Cl 117/63, 117/93, 117/102 R, Stephen Grace 117/107.2 R, 117/130 R, 117/16OR [51] Int. Cl C23c 3/04, (323a 17/02 57 ABSTRACT [58] Field of Search 117/93, 107.2 R,

1 [7/130 R 160 R 63 An electroless process for deposltmg elemental metallic coatings on solid substrates. The process comprises [561 12311115,: 2111135312S521312111.;7113113 155113: UNITED STATES PATENTS to sufficient energy to deposit the elemental form of the 51 al. n 1 R X metal on the ubstrate 3,434,879 3/1969 Langley 117/160 R X 3,462,288 8/1969 Schmidt et al. 117/107.2 R X 22 Claims, N0 Drawings DEPOSITION OF THIN METAL FILMS BACKGROUND OF THE INVENTION The present application is a continuation-in-part of copending application, Ser. No. 783,164, filed Dec. 6, 1968, now abandoned, by Richard E. Ridenour and Kenneth O. Groves.

There is a need for an economical method for depositing thin, uniform, coherent metal coatings such as for example, refractory metals i.e., tantalum, niobium and tungsten on various solid substrates, such as other metals, resin films and the like. Such coatings are employed to protect the substrate because of their superior hardness, high melting points, and chemical inertness; to provide electro conductivity and to provide decoration.

Several processes are now in use for depositing various primary metals on substrates. Most of these methods, however, have certain disadvantages associated with them. Physical vapor deposition (vacuum metallization) has been used occasionally to plate articles with metals, such as refractory metals. This process, however, has a disadvantage of requiring expensive, hard to manipulate, high vacuum equipment and is primarily useful for plating surfaces at right angles to the metal beam. Also, extremely high temperatures usually must be employed in this process. A second method concerns the chemical vapor deposition of certain metals. This process involves vaporizing a metal halide e.g. a refractory metal halide, into a stream of hydrogen gas in a nitrogen atmosphere and passing the resultant gaseous mixture over a heated substrate. Although this process has been quite successful, it still has certain disadvantages such as for example, the inclusion of nitride, halide and hydride impurities in the coating which have a tendency to reduce the usefulness of the coatings. Other methods have included the thermodecomposition of volatile metal carbonyls, U.S. Pat. No. 2,523,46 l; reaction with the substrate, sulfonation; and sputtering, i.e., an electron discharge effect. All of these methods, however, have not been completely successful because of the various indicated disadvantages. Also, various processes have been developed for depositing metal coatings from the decomposition of metal hydrides. In one of these processes, a substrate is heated to the decomposition temperature of the metal hydride in an atmosphere containing a volatile metal hydride to deposit the metal. Coatings of titanium, boron, aluminum and copper have been formed by this process. This process suffers from disadvantages such as, the requirement for high operating temperatures and the formation of non-uniform and nonadherent coatings and the like.

It has now been discovered that metal coatings can be provided on a wide range of substrate materials including, in some instances, heat sensitive substrates such as wood, paper and the like by an electroless method. Both single metal coatingsand mixtures of metals can be plated by the present process. With certain combinations of metals, temperatures below those normally required for the decomposition of certain metal hydrides can be employed.

SUMMARY The present invention concerns a process for depositing metallic coatings on substrates. The process comprises, preparing a hydride of the primary heavy metal element to be deposited in situ on the surfaceof the substrate and decomposing the hydride to form a metallic coating. The hydride is formed in situ by reacting aluminum hydride with at least part of a primary heavy metal compound in contact with the surface of the substrate to be coated. At least part of the so formed primary metal hydride is then subjected to sufficient energy, e.g. heat, to deposit the elemental form of the primary metal on the substrate. As will be more fully explained hereinafter, coatings containing primary metalaluminum mixtures can also be prepared by the method of the present invention.

PREFERRED EMBODIMENTS In the practice of one embodiment 'of the present in vention, a substrate is contacted with a liquid dispersion of a primary metal compound containing the primary metal ion to be plated, e.g. CuCl in diethyl ether. The solvent is then removed, such as by evaporation, to deposit an uniform layer of the primary metal compound on the surface of the substrate. The primary metal compound is then contacted with a liquid dispersion containing an aluminum hydride to form the hydride of the primary metal. The coated substrate is subjected to a source of energy, e.g. heat, sufficient to deposit the elemental form of the primary metal on the substrate.

The order in time at which the primary metal compound and aluminum hydride are deposited on the substrate is not critical. Thus, the reverse of the above order of deposition is equally satisfactory.

To achieve metallic coatings substantially free of metallic aluminum, aluminum by-product compounds formed during the preparation of the primary metal hydrides are removed from the substrate material such as by washing it with a solvent in which the aluminum by product is soluble following the formation of the primary metal hydride and prior to the deposition of the primary metal. Since most metal hydrides, other than aluminum and magnesium, are insoluble in most organic solvents the solvent employed is one in which the aluminum by-product compound, e.g. AlCl,, is soluble and which is also unreactive with the substrate and primary metal hydrides. To ensure a substantially aluminum-free coating, the aluminum hydride is preferably employed in at least an amount sufficient to react with the metal hydride to form the corresponding metal hydride, but not sufficient to exceed that stoichiometrically required to form the metal hydride of the primary metal to be plated. A stoichiometric amount of aluminum hydride is that amount of aluminum hydride which will substantially entirely react with the heavy metal compound, that is, substantially no unreacted aluminum hydride is present after completion of said reaction.

As indicated, however, coatings comprising a mixture of at least one primary metal and aluminum can be prepared. The mixed coatings are prepared by not removing aluminum by-product compounds from the substrate material. Such mixed metal coatings can also be prepared by employing a greater than stoichiometric amount of an aluminum hydride when preparing the hydride of the primary metal; In the second method other aluminum by-product compounds produced upon the formation of the metal hydride can. then be removed if desired. The primary metal and aluminum are then deposited by subjecting the primary metal hydride and aluminum hydride to sufficient energy e.g.

heat, to decompose the most stable hydride present on the substrate.

It has been found that in some instances the presence of certain primary metal ions will catalyze the decomposition of aluminum hydrides, thereby allowing the use of lower levels of energy, e.g. a lower decomposition temperature, than normally required. For example, AlH usually decomposes at about 180 C but in the presence of copper metal it has been found that an aluminum hydride will decompose to produce metallic aluminum at about 120 C. Therefore, certain mixtures of aluminum and primary metals can be deposited at temperatures lower than the normal decomposition temperatures by employing a greater than catalytic amount of a primary metal compound found to also have a catalytic effect. Also, catalytic quantities of primary metals found to act as catalysts can be employed to catalyze the deposition of other primary metalaluminum mixtures.

Metal compounds found to catalyze the decomposition of aluminum hydrides are compounds of the metals Ti, Zr, I-If, V, Nb and Ta. These metals may be codeposited with aluminum by employing greater than catalytic amounts thereof, or they can be employed as catalysts in the deposition of other primary metalaluminum mixtures. In either instance, it is found that the presence of these metals will reduce the energy, e.g. heat, required to deposit the aluminum.

Substantially any normal solid material which is stable under the decomposition energy employed, is suitable as a substrate. For example, metals such as iron, magnesium, brass and copper, polymers such as polyolefins,.polyamides and polymeric fluorocarbons, glass, paper, cloth, carbon and graphite, wood, ceramics and the like can all be plated with a primary metal or primary metal-aluminum mixture, by the process of this invention. The nature of the surface being plated determines to a large extent the brightness of the coating. In general, the use of a smooth, non-porous surface such as found on most metals and some polymer films produces a brighter coating than will a relatively porous surface such as the surfaces of paper or cloth. On the surfaces of some polymers such as polyethylene, polytetrafluoroethylene, acrylonitrile-butadienestyrene terpolymers and polypropylene, it has been found that even better adhesion of the coating is achieved if the surface has been made more polar e.g., by sulfonation, corona discharge and the like, prior to the coating thereof. Various shaped objects may also be coated by the process such as, for example, whisker materials, reflectors, fiber materials, automobile trim and other decorative objects.

The term aluminum hydride" is used herein in its broad sense and is meant to include any hydride compound which contains at least one aluminum atom to which at least one hydrogen atom is directly bonded and includes both the solvated and non-solvated forms of those aluminum hydrides occurring in both forms. Included, therefore, are aluminum trihydride, the substituted aluminum hydrides such as those having the empirical formula AlH,,X wherein X is a halogen, or -OR group or an -R, group (wherein R and R, are alkyl, substituted alkyl, aryl or substituted aryl groups) and n has a numerical value equal to or less than 3. Also included are the complex aluminum hydrides such as LiAlI-I NaAlH Mg(AlI-l and the like and complex substituted aluminum hydrides such as those having the empirical formula M(AlH,,,X -m wherein X has the definition given above, m has a numerical value equal to or less than 4 and M is a metal or mixture of metals, preferably an alkali or alkaline earth metal and a" has a numerical value equal to the valence of M. Of particular utility are the relatively simple aluminum hydrides containing at least two hydrogen atoms attached to the aluminum, e.g., AlH All-l Br, LiAlH and the like. Mixtures of the various aluminum hydrides may also be employed.

It is usually desirable for ease of application to employ the aluminum hydride in a solvated form. Compounds known to solvate or form complexes with the aluminum hydrides include ethers and other oxygencontaining organic compounds, and compounds containing a functional group such as a divalent sulfur atom, or trivalent nitrogen or trivalent phosphorus atom which is capable of allowing the solvation of an aluminum hydride with such compound. It is usually preferred that the solvate be an etherate and a wide variety of ethers containing from about 2 to about 20 carbon atoms are suitable. Usually the lower aliphatic ethers such as ethyl, propyl, or butyl ethers are employed but those containing an aromatic group such as methylphenyl ether, ethylphenyl ether, propylphenyl ether or the alicyclic ethers such as tetrahydrofuran and the like may be employed.

In general, to achieve ease and uniformity of application of the aluminum hydride, any solvent or mixture of solvents or suspending agents for the aluminum hydride may be employed which will not react with the aluminum hydride beyond the formation of a complex or solvate. Suitable solvents include aromatic hydrocarbons such as benzene, toluene, and xylene, aliphatic hydrocarbons such as hexane, ethers, tertiary amines and the like.

The primary heavy metals and mixtures thereof which may be plated by this method consist of metals, other than aluminum, which form compounds which will react with an aluminum hydride to fonn the corresponding heavy metal hydride compound. The elements Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Ga, In, T], Sn and Pb are generally suitable for use as the primary heavy metals in the present invention. To obtain a more adherent metal coating on the substrate the heavy metal compound is at least partially, and preferably substantially entirely, soluble in the solvent employed for the aluminum hydride.

The primary metal compound is usually dissolved in a suitable solvent and the solvent containing the primary metal compound is applied to the substrate material. It is preferable that the primary metal be in the form of a compound which is soluble to the extent of at least 1 X 10" weight per cent of the solvent employed, usually solutions from 0.05 to 0.2 molar with respect to the metal compound are employed while 0.001 to 5.0 molar solutions can be employed. Such compounds as ZrCl NbCl VOCl,, VOCl,, TlCl4'2[(CzH5)2O], TlCl3, TiCl4, TiBr4, Til4, VCl4, I 2 2 Ti9 2 Q 7. 1TiC K AgClQCTCTQ FeCl alias 1e like have proved effec tive. Normally the halides of the indicated primary metals are preferred e.g. the chlorides, bromides and oxychlorides of titanium, niobium, vanadium, iron, copper, tantalum, cadmium, and the like. Additionally, the primary heavy metal compounds having a metal to carbon, oxygen, nitrogen, sulfur, or halide bond, which are at least partially soluble in a solvent for aluminum hydride and react with aluminum hydride to form a hydride including the heavy metal, are employable in the claimed process. More specifically, compounds with a heavy metal to carbon bond such as cobalt octacarbonyl, dimethyl-mercury, cupric cyanide, and diphenylmercury; a metal to oxygen bond such as cobalt (Ill) ace tate, tetraethoxy titanium, tetra(diethylhydroxylamino) tin, tetraphenoxy tin, trimethylplatinum acetylacetonate, and titanium oxytrichloride; a metal to nitrogen bond such as thoric nitrate, tetrapyridine cupric fluosilicate, silver nitrate, and auric cyanide; a metal to sulfur bond such as nickel (IV) adducts of dithiobenzoic acid or o-aminothiophenol, and manganese (II) sulfate; and a metal to halogen bond such as nickel (Il) fluoride, cupric chloride, mercuric bromide,

and nickel (II) iodide are illustrative of metal compounds satisfactory in the claimed process.

The primary metal compounds are preferably applied to the substrate first. However, the aluminum hydrides can be applied first if desired. The primary metal and aluminum hydride compounds are preferably applied as a liquid solution or suspension or, where the nature of the metal and the substrate permit, deposited by vapor deposition. Preferably, however, the substrate is contacted with a sufficient quantity of a solution of the primary metal compound to wet the surface of the substrate. The solvent for the primary metal compound is then removed, e.g. by evaporation, leaving the primary metal compound substantially uniformly dispersed on the substrate. When an aqueous solution or suspension of the primary metal compound is applied to the substrate, essentially all of the water is removed from the substrate prior to contacting at least part of the metal compound contacted substrate with aluminum hydride. it has been found that the uniformity of distribution of the primary metal compound on the substrate has a significant effect on both the uniformity and thickness of the metal plate. It is, therefore, desirable to apply the metal compound to the substrate in a manner which will assure relatively uniform distribution. The thickness of the metal coating can be varied for example by employing different concentrations of solutions and/or by repeating the plating procedure.

For substrates having surface characteristics making uniform distribution of the primary metal compound or aluminum hydride solution difficult to achieve (such as magnesium metal and some polymers,) it has been found advantageous to add to the solutions a small amount, e.g., from about 0.0001 to about 5.0 weight per cent, of a wetting agent. Suitable wetting agents include, for example, stearates such as sodium or aluminum stearate or aluminum alkoxides such as aluminum isopropoxide.

Solvents for the primary metal compounds are those normally liquid materials which will sufficiently dissolve the primary metal compounds, which will not adversely effect the substrate, and which will not change the anion of the primary metal sufficiently to render it insoluble. Suitable solvents include organic solvents e.g. non-reactive solvents such as benzene, hexane, and halogenated hydrocarbons; reactive solvents such as alcohols, aldehydes, ketones, mercaptans and carboxylic acids; and coordinating solvents such as ethers, ni-

triles, amides and amines. Mineral acids can also be employed.

By application of the primary metal compounds to only selected areas of the substrate, it is possible to form a metal plate only on such selected areas. In this manner, ornamental designs, outlines, printed circuits and the like may be produced. Likewise, all or a portion of a selected substrate may be coated to enhance the ability of such surface to adhere to other materials. Of particular utility is the coating of glass, ceramic, metal or polymer surfaces to enhance their bonding to adhesive polymers and copolymers such as the copolymers of ethylene and acrylic acid.

The mechanism of the plating reaction is theorized as follows. It is thought that the aluminum hydride compound reacts with primary metal compounds to produce a metal hydride compound and either a soluble or volatile by-produce aluminum compound. The application of energy, e.g. heat, to the primary metal hydride then decomposes the hydride to deposit primary metal on the substrate with a liberation of free hydrogen gas and other volatile compounds. Actual practice has shown that this is probably the nature of the reaction process, however, it is understood that we are not limiting our invention by the theory of the reaction process involved.

Heat is preferably employed as the source of energy. A temperature equal to the decomposition temperature of the primary metal hydride to be deposited is employed. For example, if copper is to be plated, a temperature of about 60 C is required. Alternatively, other forms of energy such as for example, actinic light, e.g. ultraviolet light, or high energy radiation such as electron bombardment may be employed to produce rapid plating at room temperature. Likewise, combinations of such forms of energy may be employed.

The process as defined herein can be a continuous operation for the coating of various films, webs, paper, fibers, metals and the like. Also, it may be employed to coat various other irregular objects such as, whisker materials, beads, powders, various: forms of reflectors for lights, piping and the like.

The following examples are included herein to facilitate a more complete understanding of the invention but it should be understood that the invention is not limited to the specific embodiments incorporated therein. In these examples [Lg/i11 means micrograms per square inch.

EXAMPLE 1 Sheets of a polyester composition, 2 mil. thick, were dipped into a 0.05 molar solution of a primary metal compound consisting of CuCl, in anhydrous methanol. Upon evaporation of the solvent, a thin film of CuCl, was left on the sheets. This coating was done in a dry atmosphere to prevent absorption of water vapor by the hygroscopic CuCl and subsequent beading on the surface of the film.

Next, the CuCl, coated sheets were dipped into a 0.2 molar AlH in anhydrous diethyl ether solution. At this point, a blackening of the CuCl, coating was noted, indicating the formation of Cu H,

0n heating the sheets for from 10 to 30 seconds in a convection oven at C, an adherent, mirror-like coating, appearing as faintly gold colored aluminum, was obtained.

Analysis by X-ray fluorescence showed 60 p.g/in of copper, and 150 ag/in of aluminum.

EXAMPLE 2 Substitution of a 0.05M solution of CuCl -6H O into the procedure of the first Example, and drying the sheets for about one minute at 1 10 C prior to the All-l treatment gave results similar to those of Example 1.

EXAMPLE 3 Substitution of a 0.05M solution of CuCl in 80 percent ether, 20 percent methanol for the anhydrous methanol solution in the procedure of Example 1 showed marked improvement in the uniformity of the plate, probably due to the more rapid rate of evaporation of the solvent.

EXAMPLE 4 Sheets of brass, glass and polyethylene were plated by the procedure described in Example I, and similar coatings were produced.

EXAMPLE 5 Substitution of a 92.5 percent diethyl ether 7.5 percent methanol mixture, to which had been added from i to 20 drops (per 100 ml) of a surfactant consisting of an alcohol end blocked polyether, for the methanol solvent in the procedure of Example I, gave excellent uniformity of coatings with most types of substrates and strata.

An added advantage of the use of a surfactant was that thin layers of metal compounds could be affected without the use of a dry atmosphere even with such hygroscopic materials such as CuCl EXAMPLE 6 A 0.2M solution of CuCl, in 90 percent ether-l per cent methanol was used to coat 2 mil. thick polyester sheets in a manner similar to that described in Example 1.

Some of these sheets were then dipped into a 0.2 molar All-l, in anhydrous diethyl ether solution. At this point, a marked blackening of the CuCl was noted, indicating formation of Cu,l-l,.

The sheets were then rinsed in ether to remove aluminum-containing compounds.

On heating briefly to 1 10 C the Cu l-l, decomposed to give lustrous black coatings which oxidized on exposure to atmosphere oxygen for about hours, giving a transparent yellow coat. This coat analyzed as pure CuO by X-ray fluorescence.

An analysis of the sheets before oxidation showed Lg/in of aluminum, and 620 ug/in of Cu. This method indicates that with stoichiometric or less quantities of aluminum hydride compounds and the removal of aluminum by-product compounds, a substantially single metal coat can be formed on the substrate material.

EXAMPLE 7 Using the procedure of Example 6, but omitting the ether wash between the application of All-l, and heating, yielded a dark mirror finish which did not yellow on exposure to the atmosphere. Analysis by x-ray fluorescence showed 160 ,ug/in of Al and 700 [Lg/in in Cu.

EXAMPLE 8 Substitution of 0.5M (iBu), All-l (di-isobutylaluminum hydride) in hexane, for the All-l in the procedure of Example 6, gave sheets with coatings having similar characteristics to those in Example 6. Analysis by x-ray fluorescence showed 50 ptglin of Al and 930 ;4.g/in of Cu.

EXAMPLE 9 A 0.05M solution ofa primary metal compound consisting of CdCl in methanol was substituted for the CuCl solution in the procedure of Example 1. On heating the coated substrate at a temperature of from C to C mirror-like coatings were obtained. Analysis of the coating by x-ray fluorescence showed 140 ug/in of Cd, and 250 pg/in of Al.

EXAMPLE 9-B Substitution of Cdl, (0.05M in ether) for the CdCl, in the procedure of Example 9, gave similar coatings.

EXAMPLE l0 Substitution of AgNO PbCl,, and HgCl, for the CuCl in the procedure of Example 1, gave coatings of Ag, Pb, and Hg, but apparently the All-l did not decompose in the presence of these metals at temperatures up to 150 C.

EXAMPLE 11 A 0.1M solution of CrCl;-2HON=C in 95% ether, 5 percent methnol was used to coat 2 mil. polyester sheets. The procedure was similar to that employed in Example 1 and mirror-like coatings were produced on heating the coated sheets to 140 C. Analysis by X-ray fluorescence showed 200 ag/in of Cr and 220 p.g/in of Al.

EXAMPLE 12 Prior treatment of the polyester sheets in Example 1 l with a .025M solution of TiCl, in ether, resulted in'a lowering of the temperature required to plate out the metals from 140 to C.

Analysis by x-ray fluorescence showed 250 rig/in of Cr, 260 p.g/in of Al and 16 p.g/in in Ti.

EXAMPLE 13 EXAMPLE 14 A 0.1M solution of FeCl, in methanol was used to coat 2 mil polyester sheets. Upon treatment as in Example 1, mirror-like finishes were obtained which analyzed 230 ug/in of Fe and 115 p.g/in of Al.

The temperature required to obtain plating was about C.

EXAMPLE l5 Substitution of a 0.1M solution of ZnCl, in 85 percentethe lS ercent methanol into the procedure of Example 1, gave mirror-like finishes. The coatings analyzed 340 ng/in of Zn and 70 g/in of Al by X-ray fluorescence.

The temperature required to plate was 145 C.

EXAMPLE 16 A 0.1M solution of MnClin methanol was used in the procedure described in Example 1. On heating to 125 C, dark, lustrous plates were obtained, which rapidly flaked off on exposure to the atmosphere. Analysis of the inhydrolyzed material showed 300 tglin of A], and 65 [Lg/i11 of Mn (x-ray fluorescence).

EXAMPLE 17 A 0.3M solution of CoCl -6H O in acetone was used in the procedure as defined in Example 1, after prior drying at 1 10 C to dehydrate the metal. The temperature required for plating was 120' C.

Analysis by x-ray fluorescence showed 710 [Lg/i11 of Co and 220 [Lg/i11 of Al.

EXAMPLE 18 A 0.2M solution of Ta (OCH CH Q, (tantalum pentoethylate) in benzene was substituted into the procedure of Example 1. At about 145 C, shiny mirror-like plates were obtained, analyzing 650 ug/in of Ta and 150 ag/in of Al.

EXAMPLE 19 Two mil. polyester sheets were dipped into a 0.0125M solution of TiCI in ether and dried of solvent.

Next the sheets were dipped into 0.2 molar AlH in anhydrous diethyl ether and air dried, then dipped into 0.2M SnCl, in hexane and heated briefly at 140 C.

Plates thus obtained had mirror finishes and X-ray fluorescence showed 70 [Lg/i11 A1, 150 [Lg/i11 of Sn and 19 ng/in of Ti. The titanium compound served as a catalyst in the example allowing the use of a lower decomposition temperature.

EXAMPLE 20 On reversing the order of application of SnCl, and All-I and rinsing with ether prior to heating, in the procedure of Example 19, mirror coatings were obtained which analyzed 90 ag/in of A1, 310 y.g/in ofSn, and 17 ig/in of Ti by X-ray fluorescence.

What is claimed is: l. A process for depositing a metal coating onto a substrate which comprises the separate steps of:

contacting a substrate with a compound of a heavy metal selected from the group consisting of Se, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sn, In, Cd, Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Y, La, Hf, Ta, W, Re, 0s, Ir, Pt, Au, Hg, Tl, and Pb, the compound containing as an anion a halide, oxyhalide or nitrate ion and being at least partially soluble in at least one solvent for aluminum hydride and reactive with aluminum hydride;

contacting the substrate with a sufficient amount of an aluminum hydride to react with at least part of the heavy metal compound to form the corresponding heavy metal hydride; and

subjecting at least part of the aluminum hydride and heavy metal compound contacted substrate to a source of energy sufficient to form a coating containing at least the heavy metal on the subjected substrate.

2. The process of claim 1 wherein:

a the aluminum hydride is used in an amount at least sufficient to react with the metal compound to form the corresponding heavy metal hydride up to about the amount of aluminum hydride to stoichiometrically react with the metal compound to form the corresponding heavy metal. hydride and aluminum compound and deposit the heavy metal hydride on the substrate;

b contacting at least part of the contacted substrate with a solvent for the aluminum compound to remove aluminum compound from the substrate;

c subjecting at least part of the substrate contacted in Step (b) to a source of energy sufficient to form a metal coating on the subjected substrate containing the elemental form of the heavy metal.

3. The process of claim 2 wherein in Step (a) the substrate is contacted with an aluminum hydride solution, the solvent thereof being a mutual solvent for the aluminum hydride and the heavy metal compound.

4. The process of claim 2 wherein the energy comprises heat.

5. The process of claim 2 wherein the energy cornprises actinic light.

6. The process of claim 2 wherein the energy comprises high energy radiation.

7. The process of claim 2 wherein the metal compound is applied to the substrate as a liquid suspension containing the metal compound and the aluminum hydride is contacted with the metal compound as a liquid suspension containing aluminum hydride.

8. The process of claim 2 wherein:

a at least a portion of the metal compound comprises at least a catalytic amount of a compound contain ing a heavy metal selected from the group consisting of Ti, Zr, Hf, V, Nb, or Ta.

9. The process of claim 1 wherein the heavy metal is selected from the group consisting of Sc, Y, La, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, C o, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Ga, In, T], Sn, and Pb and aluminum hydride is used in a greater than stoichiometric amount.

10. The process of claim 9 wherein the substrate is also contacted with at least aca'talytic amount of a compound of a heavy metal selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta.

11. The process of claim 9 wherein the substrate is contacted with an aluminum hydride solution, the solvent thereof being a mutual solvent for the aluminum hydride and the heavy metal compound.

12. The process of claim 9 wherein the energy comprises heat.

13. The process of claim 9 wherein the energy comprises actinic light.

14. The process of claim 9 wherein the energy comprises high energy radiation.

15. The process of claim 9 wherein the metal compound is applied to the substrate as a liquid suspension containing the metal compound and the aluminum hydride is contacted with the metal compound as a liquid suspension containing aluminum hydride.

16. The process of claim 9 wherein said substrate is also contacted with a catalytic amount of substrate is also contacted with a catalystic amount of at least one compound of a heavy metal selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta.

21. The method of claim 9 wherein the substrate is first contacted with the heavy metal compound.

22. The process of claim 1 including sequentially contacting the substrate with the heavy metal compound, contacting the substrate with the aluminum hydride and then subjecting the aluminum hydride and heavy metal compound to a source of energy. 

2. The process of claim 1 wheRein: a the aluminum hydride is used in an amount at least sufficient to react with the metal compound to form the corresponding heavy metal hydride up to about the amount of aluminum hydride to stoichiometrically react with the metal compound to form the corresponding heavy metal hydride and aluminum compound and deposit the heavy metal hydride on the substrate; b contacting at least part of the contacted substrate with a solvent for the aluminum compound to remove aluminum compound from the substrate; c subjecting at least part of the substrate contacted in Step (b) to a source of energy sufficient to form a metal coating on the subjected substrate containing the elemental form of the heavy metal.
 3. The process of claim 2 wherein in Step (a) the substrate is contacted with an aluminum hydride solution, the solvent thereof being a mutual solvent for the aluminum hydride and the heavy metal compound.
 4. The process of claim 2 wherein the energy comprises heat.
 5. The process of claim 2 wherein the energy comprises actinic light.
 6. The process of claim 2 wherein the energy comprises high energy radiation.
 7. The process of claim 2 wherein the metal compound is applied to the substrate as a liquid suspension containing the metal compound and the aluminum hydride is contacted with the metal compound as a liquid suspension containing aluminum hydride.
 8. The process of claim 2 wherein: a at least a portion of the metal compound comprises at least a catalytic amount of a compound containing a heavy metal selected from the group consisting of Ti, Zr, Hf, V, Nb, or Ta.
 9. The process of claim 1 wherein the heavy metal is selected from the group consisting of Sc, Y, La, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Ga, In, Tl, Sn, and Pb and aluminum hydride is used in a greater than stoichiometric amount.
 10. The process of claim 9 wherein the substrate is also contacted with at least a catalytic amount of a compound of a heavy metal selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta.
 11. The process of claim 9 wherein the substrate is contacted with an aluminum hydride solution, the solvent thereof being a mutual solvent for the aluminum hydride and the heavy metal compound.
 12. The process of claim 9 wherein the energy comprises heat.
 13. The process of claim 9 wherein the energy comprises actinic light.
 14. The process of claim 9 wherein the energy comprises high energy radiation.
 15. The process of claim 9 wherein the metal compound is applied to the substrate as a liquid suspension containing the metal compound and the aluminum hydride is contacted with the metal compound as a liquid suspension containing aluminum hydride.
 16. The process of claim 9 wherein said substrate is also contacted with a catalytic amount of substrate is also contacted with a catalystic amount of at least one compound of a heavy metal selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta.
 17. The method of claim 1 wherein the aluminum hydride is aluminum trihydride.
 18. The method of claim 2 wherein the aluminum hydride is aluminum trihydride.
 19. The method of claim 9 wherein the aluminum hydride is aluminum trihydride.
 20. The method of claim 1 wherein the substrate is first contacted with the heavy metal compound.
 21. The method of claim 9 wherein the substrate is first contacted with the heavy metal compound.
 22. The process of claim 1 including sequentially contacting the substrate with the heavy metal compound, contacting the substrate with the aluminum hydride and then subjecting the aluminum hydride and heavy metal compound to a source of energy. 